Refrigeration apparatus with defrost control means



Nov. 13, 1962 E. J. MOORMAN 3,063,250

REFRIGERATION APPARATUS WITH DEFROST CONTROL MEANS Filed Aug. 19, 1960INVENTOR. E ar/ J. Moorman BYZZMXW His Attorney United States Patent3,063,250 REFRIGERATION APPARATUS WITH DEFROST CONTROL MEANS Earl J.Moorman, Dayton, Ohio, assignor to General Motors Corporation, Detroit,Mich., a corporation of Delaware Filed Aug. 19, 1960, Ser. No. 50,698 5Claims. (Cl. 62-155) This invention relates to refrigerating apparatusand more particularly to a control for use in defrosting the coolingcoil of a refrigerator.

In modern refrigerators where a fan is utilized to circulate a largevolume of air from the food storage compartment over the evaporator andwherein the evaporator is periodicallydefrosted by means of theapplication of electric heat to the evaporator, it becomes essential toavoid adding heatto the food compartment during or immediately followingthe defrost period.

It is an object of this invention to provide a simple and inexpensive,yet reliable, control which. will prevent the operation of theaircirculating fan at the end of the defrost cycle before the evaporatorhas had a chance to be cooled down.

Thus, it is an object of this invention to provide a control wherein therefrigeration system begins operating at the completion of the defrostcycle before the fan circulates air from the evaporator compartment intothe food storage compartment.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawing wherein a preferred embodiment of the present invention isclearly shown.

In the drawing:

The drawing shows somewhat schematically a refrigerator embodying theinvention.

Referring now to the drawing wherein a preferred arrangement has beenshown, reference numeral generally designates a refrigerator cabinethaving a food storage compartment 12 which is adapted to be refrigeratedby means of an evaporator 14 which for purposes of illustration has beenshown located in an air duct 16 adjacent the food storage compartment12. While the compartment 12 is intended to represent the freezercompartment in a refrigerator, the invention could also be used in astandard home refrigerator wherein forced air circulation is used forcooling the food compartment. The evaporator 14 forms a part of aconventional refrigerating system including a compressor 18 whichwithdraws vaporized refrigerant from the evaporator 12 and dischargescompressed refrigerant into the condenser 20 from whence the liquidrefrigerant flows to the evaporator 12 through a capillary tube type ofrestrictor 22. A fan 24 is used to circulate air from the foodcompartment over the evaporator which serves to cool the air beforebeing returned to the food compartment.

The evaporator 12 must be defrosted from time to time such as once every24 hours and for that purpose, there is provided an electric heater 26which is arranged in thermal exchange relationship with the evaporator14 and which serves to supply heat for defrosting the evaporator in amanner to be described more fully hereinafter. Power for operating therefrigerator and its controls is supplied through the power supply lines32.

A timer 28 is arranged as shown to control a doublethrow switch 30 whichserves to selectively energize either the heater circuit 26 or thecircuit for the compressor 18. This timer serves to move the switch 30from its full line position to its dotted line position once every 24hours. The switch 30 has been shown in its down position in the drawingwherein it supplies current to the line 34 which leads to thetemperature control thermostat 36. The thermostat 36 responds torefrigeration requirements and serves to close the circuit to the line 38 whenever refrigeration is required. The thermostat 36 is preferablylocated in the freezer compartment or in the return air duct and opensthe circuit to the fan and the compressor at 5 F. and recloses at +5 F.When the thermostat 36 is in the closed position, both the fan 24 andthe compressor 18 will operate.

The timer 28 moves the switch 30 from its down position to the dottedline position so as to deenergize the fan 24 and the compressor 18 andenergize the heater 26 once every 24 hours. The timer will not returnthe switch to its full line position unless the heater 26 has beenenergized for a period of 30 minutes. The heater 26 is arranged incircuit with a defrost limiter switch 40 which is normally closed at thebeginning of the defrost cycle and which opens the circuit when thetemperature of the evaporator 14 reaches a value such as 50 F.indicative of all of the frost having been melted from the evaporator.

When all of the frost has been melted from the evaporator 14, thethermostat 40 will open the circuit to the heater 26 and if this occursin less than 30 minutes after the timer closed the circuit to thedefrost heater, the solenoid coil 42 will be energized and will move theswitch 30 to its full line position. The defrost limiter switch 40shunts the coil 42 when it is in its closed position. When the circuitleading to the compressor and the fan 24 is reestablished, thecompressor will begin operating so as to render the evaporator 14effective for cooling purposes. However, the fan 24 will not startoperating until the defrost limiter switch 40 has moved to the closedposition as the result of the evaporator 14 having been cooled to atemperature such at 22 F. By virtue of the above described circuitarrangement, it is obvious that the blower or fan 24 will not be capableof circulating air over the evaporator until after the temperature ofthe evaporator has been reduced to a value such as 22 F.

While the embodiment of the present invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. In combination, a refrigerator cabinet having an insulated foodstorage compartment therein, a source of electric power, an evaporator,means including a fan for circulating air for said compartment inthermal exchange relationship with said evaporator, refrigerantliquefying means for supplying liquid refrigerant to said evaporator,temperature responsive switch means connecting said liquefying means tosaid power source, means for periodically defrosting said evaporatorincluding an electric heater arranged in thermal exchange relationshipwith said evaporator, clock operated means for initiating a defrostcycle wherein said electric heater is energized and said switch means isdisconnected from said power source, a temperature responsive defrostlimiter switch in series circuit with said heater for deenergizing saidheater at evaporator temperatures above a predetermined value, and meansfor connecting said defrost limiter switch in series with said fanwhereby said fan is deenergized when said defrost limiter switch i open.

2. In combination, a refrigerator cabinet having an insulated foodstorage compartment therein, a source of electric power, an evaporator,means including a fan for circulating air for said compartment inthermal exchange relationship with said evaporator, refrigerantliquefying means for supplying liquid refrigerant to said evaporator,means including a temperature responsive switch for connecting saidliquefying means to said power source, means for periodically defrostingsaid evaporator including an electric heater arranged in thermalexchange relationship with said evaporator, means for initiating adefrost cycle wherein said electric heater is energized and saidtemperature responsive switch is disconnected from said power source, atemperature responsive defrost limiter switch in series circuit withsaid heater for deenergizing said heater at evaporator temperaturesabove a predetermined value, and means for connecting said defrostlimiter switch in series with said fan whereby said fan is deenergizedwhen said defrost limiter switch is open.

3. In combination, a refrigerator cabinet having an insulated foodstorage compartment therein, a source of electric power, an evaporator,means including a fan for circulating air for said compartment inthermal exchange relationship with said evaporator, refrigerantliquefying means for supplying liquid refrigerant to said evaporator,temperature responsive switch means connecting said liquefying means tosaid power source, means for periodically defrosting said evaporatorincluding an electric heater arranged in thermal exchange relationshipwith said evaporator, said last named means including a single poledouble-throw switch for selectively energizing either said means forsupplying liquid refrigerant or said electric heater, timer means foroperating said single pole double-throw switch, solenoid means foractuating said single pole double-throw switch to deenergize saidelectric heater, a temperature responsive defrost limiter switch inseries circuit with said heater for deenergizing said heater atevaporator temperatures above a predetermined value, said' defrostlimiter switch serving to shunt said solenoid means when closed, andmeans for connecting said defrost limiter switch in series with said fanwhereby said fan is deenergized when said defrost limiter switch isopened.

4. In combination, a refrigerator cabinet having an insulated foodstorage compartment therein, a source of electric power, an evaporator,means including a fan for circulating air for said compartment inthermal exchange relationship with said evaporator, refrigerantliquefying means for supplying liquid refrigerant to said evaporator,temperature responsive switch means connecting said liquefying means tosaid power source, means for periodically defrosting said evaporatorincluding an electric heater arranged in thermal exchange relationshipwith said evaporator, said last named means including a single poledouble-throw switch for selectively energizing either said means forsupplying liquid refrigerant or said electric heater, timer means foroperating said single pole double-throw switch, solenoid means forcontrolling the operation of said single pole double-throw switch, atemperature responsive defrost limiter switch in series circuit withsaid heater for deenergizing said heater at evaporator temperaturesabove a predetermined value, said defrost limiter switch serving toshunt said solenoid means when closed, and means for connecting saiddefrost limiter switch in series with said fan whereby said fan isdeenergized when said defrost limiter switch is opened.

5. In combination, a refrigerator cabinet having an insulated foodstorage compartment therein, a source of electric power, an evaporator,means including a fan for circulating air for said compartment inthermal exchange relationship with said evaporator, refrigerantliquefying means for supplying liquid refrigerant to said evaporator,temperature responsive switch means connecting said liquefying means tosaid power source, means for periodically defrosting said evaporatorincluding an electric heater arranged in thermal exchange relationshipwith said evaporator, said last named means including a single poledouble-throw switch for selectively energizing either said means forsupplying liquid refrigerant or said electric heater, timer means foroperating said single pole double-throw switch, solenoid means forcontrolling the operation of said single pole double-throw switch, atemperature responsive defrost limiter switch in series circuit withsaid heater for deenergizing said heater at evaporator temperaturesabove a predetermined value, said solenoid being connected in shuntcircuit relationship with said defrost limiter switch, and means forconnecting said defrost limiter switch in series with said fan wherebysaid fan is deenergized when said defrost limiter switch is opened.

References Cited in the file of this patent UNITED STATES PATENTS2,662,380 Sutton Dec. 15, 1953 FOREIGN PATENTS 807,812 Great BritainJan. 21, 1959

